The consolidation and industrialization of the poultry industry over the last 50 years has resulted in highly concentrated regional poultry operations. Traditionally, farmers managed the manure or litter associated with poultry production by spreading it on fields. However, as the industry consolidated, operations became highly regionally concentrated, and cropland diminished, this waste disposal method became less viable. For example, in the Maryland-Delaware region, 523 million chickens are now produced annually, generating approximately 42 million cubic feet of chicken waste each year, such that chickens outnumber people in the region by as much as 400 to 1. This high concentration of waste causes eutrophication (e.g. nitrogen, phosphorus), particularly along the shores of the Chesapeake Bay, the largest estuary system in the United States, creating an urgent need for efficient, clean, environmentally friendly chicken waste disposal approaches.
The United Nations and The U.S. Federal Government have identified agriculture as the biggest user of water and a major polluter of water. In fact, agriculture has been identified as the single largest source of pollutants for rivers, lakes, and estuaries in the U.S. The industrialization of agriculture has resulted in such high concentrations of animal waste that conventional disposal methods are no longer adequate or viable (e.g. spreading on fields). Thus, there is an urgent need for environmentally safe and economically viable approaches to disposing of agricultural waste. This need in combination with global demand for clean, low-cost, renewable energy has fueled interest in biomass-to-energy conversion technologies, including for use in disposing of high concentrations of animal waste, which approach becomes even more appealing given recently implemented regulations that prohibit the use of chicken litter as fertilizer on significant acreage. However, due to the low energy density of biomass, the economics of biomass-to-energy operations have been challenging (i.e., fuel collection and transportation costs can be high relative to energy density; high moisture content adds to transportation costs and reduces burn efficiencies). Thus, there remains a need for solutions that can reduce the cost of converting biomass to energy and/or increase the efficiency of the combustion process.
Fluidized bed combustion systems are often used for burning biomass fuel. Most of the existing fluidized bed combustion apparatus known to the inventor have only a single level secondary injection of air in the fixed tangential direction to facilitate a turbulent or swirling flow, as shown in U.S. Pat. No. 5,105,917 to Harada et al., and in U.S. Pat. No. 8,161,917 to Yang et al., the specifications of which are incorporated herein by reference in their entireties. Certain systems disclose multiple secondary air supply ports, such as the system shown in European Patent Publication No. 0 458 967 A1. Still other systems disclose methods for incinerating waste using a two-level swirling flow fluidized bed without tangential flow for suppressing re-synthesis of dioxins produced during incineration and the removal of a suspended particulate material, such as the system disclosed in International PCT Publication No. WO/2010/010630. The specifications of each of the foregoing references are incorporated herein by reference in their entireties. However, widespread commercial acceptance of such prior systems has been lacking, due to an inability to reach sufficiently high combustion efficiencies and minimization of noxious emissions. Thus, there remains a need in the art for fluidized bed combustion systems and methods capable of efficiently and cleanly disposing of biomass materials.